1. Field of the Invention
The invention relates to addition-crosslinkable silicone compositions and the silicone elastomers obtainable therefrom.
2. Description of the Related Art
It is known that addition of polydiorganosiloxanes having alkenyl groups in the chain to alkenyldiorganosiloxy-terminated polydiorganosiloxanes having a viscosity of up to 200,000 mPas can give addition-crosslinkable liquid silicone rubbers (LSR compositions) which, after crosslinking, produce silicone elastomers having improved mechanical properties. This applies particularly to the tear propagation resistance in accordance with ASTM D 624 B. One way of improving the mechanical properties, in particular the tear propagation resistance, is to add polydiorganosiloxanes having alkenyl groups in terminal positions and along the chain or low-viscosity alkenyldiorganosiloxy-terminated polydiorganosiloxanes to alkenyldiorganosiloxy-terminated polydiorganosiloxanes.
EP-A-305073 describes improvement of the mechanical properties, in particular the tear propagation resistance, by addition of a polydiorganosiloxane which bears vinyl groups both at the end of the chain and also in the chain and has a viscosity of 100,000 to 200,000 mPas to a vinyl-terminated polydiorganosioxane having a viscosity of from 20,000 to 200,000 mPas. This polymer combination makes it possible to obtain silicone elastomers having a tear propagation resistance of about 40 N/mm (ASTM D624) and an elongation at break of at most 580% at a hardness of about 50 Shore A.
EP-A-305073 describes improvement of the mechanical properties, in particular the tear propagation resistance, by addition of a polydiorganosiloxane which bears vinyl groups both at the end of the chain and also in the chain and has a viscosity of 100–200 000 mPas to a vinyl-terminated polydiorganosiloxane having a viscosity of from 20 000 to 200 000 mPas. This polymer combination makes it possible to obtain silicone elastomers having a tear propagation resistance of about 40 N/mm (ASTM D624) and an elongation at break of at most 580% at a hardness of about 50 Shore A.
EP-A-695787 describes improvement of the tear propagation resistance by means of a low molecular weight vinyl-terminated polydiorganosiloxane having a viscosity of from 1.0 to <50 mPas. However, the addition of such low-viscosity vinyl-terminated polydiorganosiloxanes results in a reduction in the elongation at break.